英语听力：冰河绿洲—13

Along some stretches of the riverbed were massive bones recreated here, perfectly preserved for more than 13,000 years. One of the most significant discoveries was the huge skull of an American mastodon. Mastodons, close relatives of mammoths, were widespread all over North America during the ice age. They grew over three metres tall, the size of Africa elephants today. We know a lot about the mastodons, especially their diet, thanks to the preserved dung they left behind.